Early organogenesis of many epithelial organs involves the transformation of a placode into a vesicle. During the formation of the eye, the optic vesicle invaginates to form the double layered optic cup. Several hypotheses have been advanced to explain these morphogenetic movements. These hypotheses involve the role of both cytoplasmic organelles and extracellular materials. It is probable that several forces rather than a single force are involved in the shape change. The use of an in vitro system in which invagination will occur rapidly provides a model system for dissecting out the roles of various parameters that might control the shape change. Invaginaton of the optic vesicle occurs in minutes in nutrient medium containing detergent and ATP. The effects of treatment with this medium will be assessed by transmission and scanning electron microscopy. The next step will be to investigate the effects of drug treatments on the ultrastructural changes that occur in the treated primordia. Preparations will be examined for changes in organization of microfilaments, microtubules, and other cytoplasmic organelles. Extracellular macromolecules will be examined by scanning electron microscopy after precipitation with polycations.